Could Toyota Engineers Have Anticipated Floor Mat Issues?

A June recall of Toyota's vehicles has sparked debate over how far engineers should go in designing for misuse of products. The recall urged Toyota to fix 154,000 vehicles to prevent problems that might occur when improper floor mats are used by owners. "The accelerator pedal can get stuck in the wide open position due to its being trapped by an unsecured or incompatible driver's floor mat," said a statement from the National Highway Traffic Safety Administration (NHTSA).

The latest recall, which involves the 2010 Lexus RX 350 and Lexus RX 450h, raises questions about the role of design engineers with its citing of "unsecured or incompatible floor mats." "Sometimes, owners use floor mats from another vehicle," Toyota spokesman Mike Michels told us. "Sometimes, they use aftermarket mats. We've even found carpet remnants stacked on the floor. The record was eight -- in that case, you couldn't even see the accelerator pedal."

The 2010 Lexus RX 350 was cited in a government recall related to floor mat problems. (Source: Toyota)

Use of unsecured floor mats can be a problem when they get caught on the accelerator pedal. It's not known if the mats caused any of Toyota's incidences of unintended acceleration that dominated the media two years ago. To prevent such problems in the future, however, Toyota has had to recall hundreds of thousands of vehicles. In some cases, the company's engineers re-shaped the bottom of the accelerator pedal to create more clearance. In others, they modified the plastic pad on the floor and even altered the vehicle floor pan to make more room.

Automotive experts told Design News that Toyota engineers might have been able to prevent the floor mat issues. Even though the mats may have been inappropriate for the Toyota and Lexus vehicles, they said, the problem involved interaction between just two components -- floor mat and pedal. As such, engineers probably could have imagined the potential failure modes, tested for them, and taken preventative measures.

"They should have been able to test for most of the conditions -- when the mats slide around, when they are mispositioned, when they are upside down, and even when the driver and passenger floor mats are swapped," Steven Eppinger, professor of engineering systems at Massachusetts Institute of Technology (MIT), said in an interview. "It's impossible to test for everything, but if you make your design more robust for the 50 things you can think of, then it's likely to be robust for the 20 things you didn't think of."

Although the number and severity of the owner complaints have not yet been made public, some observers believe that use of aftermarket floor mats by American consumers may have posed an unforeseen problem for Japanese designers. David Champion, senior director of Consumer Reports Automotive Test Center, told us:

They don't consider aftermarket floor mats, especially in Japan where everything is neat and tidy. There were also other issues -- like people putting rubber floor mats on top of existing floor mats. These are forms of misuse that can happen. And any misuse that would be considered normal in the US car market should have been taken into consideration.

It's hard to say if Toyota's engineers skimped over a key piece of the development process with this particular example and I'm certain there's no way an engineering team can be expected to anticipate every possible failure given the practicalities and constraints of development cycles. That said, this example points up the very key requirement to do some level of design for misuse as part of the iterative process. It's one of those areas like design for assembly and disassembly that likely gets short shrift in a lot of companies and across myriad industries--not just automotive.

Industrial workplaces are governed by OSHA rules, but this isn’t to say that rules are always followed. While injuries happen on production floors for a variety of reasons, of the top 10 OSHA rules that are most often ignored in industrial settings, two directly involve machine design: lockout/tagout procedures (LO/TO) and machine guarding.

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